1. Technical Field
The present invention is directed to the surface treatment of biomedical devices including ophthalmic lenses, stents, implants and catheters to increase their wettability.
2. Description of Related Art
Medical devices such as ophthalmic lenses made from, for example, silicone-containing materials, have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Hydrogels can absorb and retain water in an equilibrium state, whereas non-hydrogels do not absorb appreciable amounts of water. Regardless of their water content, both hydrogel and non-hydrogel silicone medical devices tend to have relatively hydrophobic, non-wettable surfaces that have a high affinity for lipids. This problem is of particular concern with contact lenses.
Those skilled in the art have long recognized the need for modifying the surface of such silicone contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of the contact lens surface improves the wettability of the contact lenses. This, in turn, is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens's susceptibility to deposition, particularly the deposition of proteins and lipids resulting from tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended wear lenses (i.e., lenses used without daily removal of the lens before sleep), the surface is especially important, since extended wear lenses must be designed for high standards of comfort and biocompatibility over an extended period of time.
Silicone lenses have been subjected to plasma surface treatment to improve their surface properties, e.g., surfaces have been rendered more hydrophilic, deposit resistant, scratch-resistant, or otherwise modified. Examples of previously disclosed plasma surface treatments include subjecting the surface of a contact lens to a plasma containing an inert gas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942; and 4,214,014); various hydrocarbon monomers (see, for example, U.S. Pat. No. 4,143,949); and combinations of oxidizing agents and hydrocarbons such as water and ethanol (see, for example, WO 95/04609 and U.S. Pat. No. 4,632,844). U.S. Pat. No. 4,312,575 discloses a process for providing a barrier coating on a silicone or polyurethane lens by subjecting the lens to an electrical glow discharge (plasma) process conducted by first subjecting the lens to a hydrocarbon atmosphere followed by subjecting the lens to oxygen during flow discharge, thereby increasing the hydrophilicity of the lens surface.
U.S. Pat. Nos. 4,168,112, 4,321,261 and 4,436,730 disclose methods for treating a charged contact lens surface with an oppositely charged ionic polymer to form a polyelectrolyte complex on the lens surface that improves wettability.
U.S. Pat. No. 4,287,175 discloses a method of wetting a contact lens that comprises inserting a water-soluble solid polymer into the cul-de-sac of the eye. The disclosed polymers include cellulose derivatives, acrylates and natural products such as gelatin, pectins and starch derivatives.
U.S. Pat. No. 5,397,848 discloses a method of incorporating hydrophilic constituents into silicone polymer materials for use in contact and intra-ocular lenses.
U.S. Pat. Nos. 5,700,559 and 5,807,636 disclose hydrophilic articles (e.g., contact lenses) comprising a substrate, an ionic polymeric layer on the substrate and a disordered polyelectrolyte coating ionically bonded to the polymeric layer.
U.S. Pat. No. 5,705,583 discloses biocompatible polymeric surface coatings. The polymeric surface coatings disclosed include coatings synthesized from monomers bearing a center of positive charge, including cationic and zwitterionic monomers.
European Patent Application No. EP 0 963 761 A1 discloses biomedical devices with coatings that are said to be stable, hydrophilic and antimicrobial, and which are formed using a coupling agent to bond a carboxyl-containing hydrophilic coating to the surface of the devices by ester or amide linkages.
U.S. Pat. No. 6,428,839 discloses a method for improving the wettability of a medical device which includes the steps of (a) providing a medical device formed from a monomer mixture comprising a hydrophilic monomer and a silicone-containing monomer; and (b) contacting a surface of the medical device with a solution including a polymer or copolymer of (meth)acrylic acid.
Typically, a medical device such as a contact lens is exposed to an aqueous environment having a pH in the range from 6.5 to 8.0 during storage in a package and during wear. A problem associated with coatings formed from a polymer or copolymer of (meth)acrylic acid is that during use of the contact lens in this pH environment, these polymers are highly ionized and have little surface activity. Therefore, the coating can be removed from the lens relatively easily thereby exposing the lens surface and resulting in a reduction in wetting and lubricity.
Accordingly, it would be desirable to provide improved biomedical devices such as a silicone hydrogel contact lens with an optically clear, hydrophilic surface film that will not only exhibit improved wettability, but which will generally allow the use of a silicone hydrogel contact lens in the human eye for an extended period of time. In the case of a silicone hydrogel lens for extended wear, it would be desirable to provide a contact lens with a surface that is also highly permeable to oxygen and water. Such a surface treated lens would be comfortable to wear in actual use and would allow for the extended wear of the lens without irritation or other adverse effects to the cornea.